1. Field of the Invention
The present invention relates to a liquid supply apparatus useful for preparing an eluting solution to be used for e.g. liquid chromatography or a reactant solution to be used for a reaction.
2. Discussion of Background
In liquid chromatography wherein a certain component in a sample solution is separated by a difference in the affinity to gel, the separation is usually substantially affected by a small change in e.g. the pH, the concentration of salts or the concentration of organic solvents in the eluting solution. Therefore, it is necessary to precisely adjust the composition of the eluting solution.
Also in the field of an analysis such as a colorimetric analysis, it is required to prepare a reactant solution with extremely high precision to control the analytical reaction precisely or to improve the reproducibility of the analysis.
However, the conventional methods for preparation of these solutions are very time-consuming and lack in precision. An example of such operational procedure will be given below.
When 1 liter of a solution comprising a 0.1M sodium dihydrogenphosphate/disodium hydrogenphosphate buffer solution (pH 5.5) and 20% methanol is to be prepared by using a 1M sodium dihydrogenphosphate (NaH.sub.2 PO.sub.4) solution (solution A), a 1M disodium hydrogenphosphate (Na.sub.2 PO.sub.4) solution (solution B), 100% methanol and distilled water, firstly an operation of alternately adding solution A and solution B followed by stirring is repeated while watching a hydrogen ion concentration meter (a pH meter) until the hydrogen ion concentration (pH) reaches 5.5 . This operation is continued until the total amount of the two solutions reaches 100 ml. Then, the electrode is taken out from the solution, and 200 ml of methanol is measured by a measuring cylinder and added to the solution. Further, 700 ml of distilled water is measured by a measuring cylinder and added to the solution. This is a common procedure for the preparation of such a solution.
In such a procedure, it takes a long time to adjust the hydrogen ion concentration in the solution to a predetermined level, as mentioned above, and it also requires a substantial labor to precisely adjust the amount of the buffer solution to 100 ml. Further, the procedure involves a number of measuring operations, whereby a number of measuring equipments are required, and the preparation and after-treatment of such equipments are time- and labor-consuming.
In order to overcome these drawbacks, it has been proposed to adjust the composition of a solution by means of a conventional supply apparatus. However, with a usual supply apparatus, the hydrogen ion concentration of the solution can not be measured. Thus, such a proposal has a serious drawback that the hydrogen ion concentration of the adjusted solution can not be made constant.